Peipei Qi

Enantioselective analysis and degradation studies of isocarbophos in soils by chiral liquid chromatography-tandem mass spectrometry.

An enantioselective method is presented for the determination of isocarbophos in soil by liquid chromatography coupled with tandem mass spectrometry. The pesticide residues in soil samples were extracted with acetonitrile, and complete enantioseparation was obtained on an amylose tris(3,5-dimethylphenylcarbamate) chiral column using acetonitrile/2 mM ammonium acetate solution containing 0.1% formic acid (60:40, v/v) as the mobile phase. The absolute configuration of isocarbophos enantiomers was determined by the combination of experimental and calculated electronic circular dichroism spectra. The method was utilized to investigate the degradation of isocarbophos in soils (Changchun, Hangzhou, and Zhengzhou) under sterilized or native conditions. Isocarbophos enantiomers were configurationally stable in the selected soils, and the pesticide degradation was not enantioselective in the sterilized condition. The degradation behavior of rac-isocarbophos was different under native conditions, with no enantioselectivity in the Changchun soil and with the S-(+)-isocarbophos enriched in the Hangzhou and Zhengzhou soils.

Environmental behavior of the chiral organophosphorus insecticide acephate and its chiral metabolite methamidophos: enantioselective transformation and degradation in soils.

Acephate is a widely used organophosphorus insecticide globally, although there are some concerns about its usage with regard to acute consumer exposure and side-effects on nontarget organisms. These concerns are always attributed to the acephate metabolite methamidophos. In the many reports about the environmental behavior of acephate and its metabolite, none pay any attention to the chirality of them. In this study, the enantiomeric transformation and degradation of acephate was investigated in three soils under laboratory conditions using enantioselective GC-MS/MS. Racemic and enantiopure compounds were incubated in separate experiments. The degradation of racemates was shown to be enantioselective in unsterilized soils but not in the sterilized soils, thus confirming the enantioselectivity was microbially based. The priority of enantiomer degradation and transformation varied among soils and racemates. R-(+)-methamidophos was enriched in the Zhengzhou soil, but degraded faster in the Changchun and Nanchang soils than its antipode. For acephate, the Nanchang soil enriched R-(+)-acephate, and S-(-)-acephate accumulated in the other two soils. Acephate and methamidophos were both configurationally stable in soil, showing no interconversion of R-(+)- to S-(-)-enantiomers, or vice versa. The conversion of acephate to methamidophos proceeded with retention of configuration. Generally, the degradation followed approximate first-order kinetics, but showed significant lag phases.

Enantioselective determination of acylamino acid fungicides in vegetables and fruits by chiral liquid chromatography coupled with tandem mass spectrometry

An efficient and sensitive enantioselective method for simultaneous determination of three acylamino acid fungicides in vegetables and fruits was presented by high-performance liquid chromatography (HPLC) coupled with tandem mass spectrometry. The three fungicides (benalaxyl, furalaxyl, and metalaxyl) residues in samples were extracted with acetonitrile containing 1% acetic acid and an aliquot was cleaned up with Si-(CH(2))(3)-NH-(CH(2))(2)-NH(2) and C(18) sorbent. Complete enantioseparation of three acylamino acid fungicides enantiomers was obtained under reversed-phase conditions on a cellulose tris (4-chloro-3-methylphenylcarbamate) column at 25°C using acetonitrile-0.1% formic acid solution (45:55, v/v) as a mobile phase. The elution orders of the eluted enantiomers were determined by a circular dichroism (CD) detector. The linearity, matrix effect, recovery, and precision were evaluated. Good linearity was obtained over the concentration range of 0.5-250 μg/L for each enantiomer in the standard solution and sample matrix calibration curves. There was no significant matrix effect for three fungicides determination based on the method. The inter-day mean recoveries, intra-day repeatability, and inter-day reproducibility varied from 81.3 to 95.7%, 2.2 to 9.4%, and 2.3 to 9.6%, respectively. The method provided high selectivity and sensitivity, and limits of quantification for enantiomers of three fungicides in vegetables and fruits were both 1 μg/kg.

Enantioselective analysis and dissipation of triazole fungicide penconazole in vegetables by liquid chromatography-tandem mass spectrometry.

Penconazole is a typical triazole fungicide, which is commonly used to control powdery mildew in vineyard and vegetable field. In this study, the enantioselective dissipation of penconazole in cucumber, tomato, head cabbage, and pakchoi was investigated by field experiments. A sensitive method for enantiomeric analysis of penconazole was established on the basis of the buffered QuEChERS sample preparation technique followed by reverse-liquid chromatography equipped with a TSQ Discovery triple quadrupole mass spectrometer and a Lux Cellulose-2 chiral column. Methanol and 2 mM ammonium acetate buffer solution containing 0.1% formic acid (70:30, v/v) were used as mobile phase at a 0.2 mL L(-1) flow rate isocratic elution. The linearity, recovery, and precision of this method were also evaluated. Finally, the results of this study demonstrated that enantioselective dissipation occurred in head cabbage and pakchoi, with the preferential degradation of (-)-penconazole, and resulting in an enrichment of the (+)-penconazole residue in the two vegetables. However, the enantioselective behavior was not observed in cucumber and tomato. More importantly, this is the first report of enantioselective behavior of penconazole, and the result may provide useful information for the risk evaluation of penconazole in food and environmental safety.

Multi-pesticides residue analysis of grains using modified magnetic nanoparticle adsorbent for facile and efficient cleanup

A facile, rapid sample pretreatment method was developed based on magnetic nanoparticles for multi-pesticides residue analysis of grains. Magnetite (Fe3O4) nanoparticles modified with 3-(N,N-diethylamino)propyltrimethoxysilane (Fe3O4-PSA) and commercial C18 were selected as the cleanup adsorbents to remove the target interferences of the matrix, such as fatty acids and non-polar compounds. Rice was used as the representative grain sample for method optimization. The amount of Fe3O4-PSA and C18 were systematically investigated for selecting the suitable purification conditions, and the simultaneous determination of 50 pesticides and 8 related metabolites in rice was established by liquid chromatography-tandem mass spectrometry. Under the optimal conditions, the method validation was performed including linearity, sensitivity, matrix effect, recovery and precision, which all satisfy the requirement for pesticides residue analysis. Compared to the conventional QuEChERS method with non-magnetic material as cleanup adsorbent, the present method can save 30% of the pretreatment time, giving the high throughput analysis possible.

Use of liquid chromatography- quadrupole time-of-flight mass spectrometry for enantioselective separation and determination of pyrisoxazole in vegetables, strawberry and soil.

The present work firstly described the enantio-separation and determination of pyrisoxazole enantiomers in vegetables, strawberry and soil samples by chiral liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS). Pyrisoxazole has two chiral carbon atoms and consists of four stereoisomers. Taking the specific optical rotation measurement and MS analysis data into consideration, the four enantiomers were discriminated as (-)-A, (+)-A, (+)-B and (-)-B corresponding to their elution order under the optimum chromatographic condition. Influences of the mobile phase and column temperature on the enantio-separation selectivity of pyrisoxazole were explored. The perfect baseline separation of pyrisoxazole enantiomers can be achieved within 10min using methanol- water (70:30, v/v) as mobile phase on chiral Lux Cellulose-3 column. The thermodynamic analysis demonstrated that the enantioseparation of (-)-A and (+)-A, (+)-A and (+)-B were enthalpy driven separation, while the enantioseparation of (+)-B and (-)-B was entropy driven separation. Under the optimum method, method validation including matrix effect, linearity, sensitivity and precision were performed. At the spiked concentration of 10, 50 and 100μgkg(-1), the recoveries of the pyrisoxazole enantiomers in cucumber, tomato, pakchoi, pepper and strawberry samples were 64.2-100% (RSD≤14%); While they were relatively higher in soil samples and all around 120% (RSD ≤10%). The limits of detection are in the range from 0.2 to 1.0μgkg(-1) for cucumber, tomato, pakchoi, pepper, strawberry and soil samples. The developed method was then utilized for monitoring the degradation kinetics of pyrisoxazole enantiomers in strawberry under field trials, which provided the environmental behavior data of chiral pyrisoxazole enantiomers and consequently for further health risk assessment of the chiral pesticides.

Citrinin Determination in Red Fermented Rice Products by Optimized Extraction Method Coupled to Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS).

A rapid and sensitive method was developed and validated for citrinin determination in red fermented rice products by liquid chromatography tandem mass spectrometry (LC-MS/MS) under the selected reaction monitoring mode. Sample preparation was especially focused, and the quantitative methods of LC-MS/MS and high-performance liquid chromatography with fluorescence detection (HPLC-FLD) were compared. In red fermented rice samples, the limit of detection was 1.0 μg/kg for LC-MS/MS compared to 250 μg/kg for HPLC-FLD, the limit of quantification was 3.0 μg/kg for LC-MS/MS compared to 825 μg/kg for HPLC-FLD. High correlation coefficient was obtained (R(2) = 0.999) within the linear range (0.1 to 100 μg/L) in the MS method. The recoveries ranging from 80.9% to 106.5% were obtained in different spiking concentrations. The average intra- and inter-day accuracy ranged from 75.4% to 103.1%, and the intra- and inter-day precisions were from 3.3% to 7.9%. The developed method was applied to 12 commercial red fermented rice products, and citrinin was found in 10 samples ranging from 0.14 to 44.24 mg/kg. Compared to traditional qualitative and quantitative methods, the newly developed LC-MS/MS method for citrinin determination includes the merits of using a small amount of extraction solvent, simple preparation steps, and high sensitivity.

Enantioselective determination of carboxyl acid amide fungicide mandipropamid in vegetables and fruits by chiral LC coupled with MS/MS

An efficient enantioselective method for the determination of mandipropamid in vegetables and fruits was presented by LC coupled with MS/MS. The mandipropamid residues in samples (potato, pepper, grape, and watermelon) were extracted with acetonitrile containing 1% acetic acid. An aliquot was cleaned up with primary and secondary amine and C18 sorbent. Complete enantioseparation of mandipropamid enantiomers in <4 min was obtained on a Lux Cellulose-2 column at 25°C using methanol with 0.1% formic acid/0.1% aqueous formic acid solution (85:15, v/v) as mobile phase. Good linearity was obtained over the concentration range of 0.5-250 μg/L for each enantiomer in the standard solution and sample matrix calibration curves. Quantification was achieved using matrix-matched standard calibration curves. The interday mean recoveries, intraday repeatability, and inter-day reproducibility varied from 76.4 to 97.1%, 3.4 to 9.4%, and 3.5 to 11.4%, respectively. The limits of quantification for mandipropamid enantiomers in vegetables and fruits were both 1 μg/kg. Moreover, the absolute configuration of mandipropamid enantiomers was determined by the combination of experimental and predicted electronic circular dichroism spectra, and the first eluted enantiomer was confirmed as (R)-mandipropamid on five chiral columns.

Exploiting pH-Regulated Dimer-Tetramer Transformation of Concanavalin A to Develop Colorimetric Biosensing of Bacteria

Gold nanoparticles (AuNPs) aggregation-based colorimetric biosensing remains a challenge for bacteria due to their large size. Here we propose a novel colorimetric biosensor for rapid detection of Escherichia coli O157:H7 (E. coli O157:H7) in milk samples based on pH-regulated transformation of dimer/tetramer of Concanavalin A (Con A) and the Con A-glycosyl recognition. Briefly, antibody-modified magnetic nanoparticles was used to capture and concentrate E. coli O157:H7 and then to label with Con A; pH adjusted to 5 was then applied to dissociate Con A tetramer to release dimer, which was collected and re-formed tetramer at pH of 7 to cause the aggregation of dextran-modified AuNPs. The interesting pH-dependent conformation-transformation behavior of Con A innovated the design of the release from the bacteria surface and then the reconstruction of Con A. Therefore, we realized the sensitive colorimetric biosensing of bacteria, which are much larger than AuNPs that is generally not suitable for this kind of method. The proposed biosensor exhibited a limit of detection down to 41 CFU/mL, short assay time (~95 min) and satisfactory specificity. The biosensor also worked well for the detection in milk sample, and may provide a universal concept for the design of colorimetric biosensors for bacteria and virus.

Enantioselective degradation of (2RS,3RS)-paclobutrazol in peach and mandarin under field conditions.

In this study we investigated the enantioselective degradation of (2RS,3RS)-paclobutrazol in peach and mandarin fruits under field conditions after foliar treatment at 500 mg active ingredient/L using a Lux Cellulose-1 chiral column on a reverse-phase liquid chromatography-tandem mass spectrometry system. Degradations of paclobutrazol in both fruits followed first-order kinetics, with half-lives of about 9 days. Initial deposits were 1.63 mg/kg on peach and 1.99 mg/kg on mandarin; terminal concentrations were lower than 0.05 mg/kg, which was acceptable in most cases. As anticipated, paclobutrazol levels in peels of mature mandarin were about 6.3 times higher than in pulp, indicating the potential risk of peel consumption. We also observed that paclobutrazol degradation in mature mandarin was relatively slow, indicating it might not be efficient enough to hold mandarin fruits on trees for lowering paclobutrazol concentrations. Significant enantioselectivity was observed: the (2R,3R)-enantiomer was preferentially degraded in mandarin (whole fruit, peels, and pulp) but enriched in peach. Because of its more rapid degradation in mandarin and the lower levels observed in pulp compared with peels, potential endocrine-related side effects due to the (2R,3R)-enantiomer pose less of a risk in mandarin than in peach.